1. Field of the Invention
Embodiments of this application relate generally to electrical circuits and input/output (“I/O”) interfaces, and, more particularly, to a method and circuit for transmitter equalization using unit- and fractional-sized subdrivers for high-speed serial interfaces.
2. Description of Related Art
Electrical circuits and data storage devices have evolved becoming faster and transmitting greater amounts of data. With the increased speed and bandwidth capabilities of electrical circuits and data storage devices, I/O interfaces must be adapted to be compatible with new system and technology requirements. As technologies for electrical and semiconductor circuits, communications and data storage devices have progressed, there has developed a greater need for reliability and stability, particularly in the area of I/O interfaces. However, voltage, current and signal transmission considerations introduce substantial barriers to controlling output amplitude for I/O interfaces. Issues such as attenuation and integrity for differential signals are particularly problematic.
Typically, in modern implementations for I/O interfaces, current-mode logic (“CML”) drivers use large numbers of parallel instances of identical unit-sized subdrivers (also called slices or drivelets) in an attempt to compensate for channel loss and signal integrity problems. However, using multiple instances of identical unit-sized subdrivers to mitigate channel loss and integrity issues is inadequate to provide required performance and yield, especially at process, voltage and temperature (“PVT”) corners. That is, variations in I/O interfaces and CML circuits due to PVT corners cause low yield and inadequate performance using state of the art solutions. Additionally, this approach requires large numbers of unit-sized subdriver slices, and this causes power dissipation issues, routing issues and excessive wiring capacitance. Excessive wiring capacitance causes reductions in driver bandwidth and difficulties in meeting transmission protocol requirements such as rise and fall times for data signals.
Embodiments presented herein eliminate or alleviate the problems inherent in the state of the art described above.